1. Field of the Invention
The present invention relates to a radiation sensing technology for sensing a radiation image.
2. Related Background Art
An X-ray imaging apparatus for obtaining a radiation image of an object by irradiating an inspection object with radiation and detecting an intensity distribution of the radiation penetrating the object, has hitherto been widely utilized in the field of industrial non-destructive inspections and in the field of medical diagnoses.
A film/screen method for X-rays is exemplified as a general method for performing the above sensing process. This is a method using a photosensitive film and a fluorescent substance having a sensitivity to the X-rays in combination.
The sensing method given above is that when irradiating the X-rays, the sheet-shaped fluorescent substances of luminous rare earth, which are arranged on both surfaces of the photosensitive film with being in contact therewith, convert the X-rays penetrating the object into visible rays, and the photosensitive film captures the visible rays. Then, a latent image formed on the film can be made visible by developing this latent image by a chemical treatment.
On the other hand, with advancements of digital technologies over the recent years, there has been a demand for a system for obtaining a high quality image of the radiation by converting the radiation image into electric signals, then executing image processing on these electric signal and thereafter reproducing them as a visible image on a CRT, etc. . . As a method of converting the radiation image into the electric signals, there has been proposed a radiation image recording/reproducing system (e.g., Japanese Patent Application Laid-Open Nos. 55-12429 and 56-11395) in which a radiation image is temporarily accumulated as a latent image in the fluorescent substance, and thereafter irradiating it pumping (excited) beams such as laser beams, etc. to photoelectrically read out the latent image and output as a visible image by.
Moreover, with advancements of semiconductor process technologies over the recent years, there has been developed an apparatus that similarly captures the radiation image by use of a semiconductor sensor. These systems have by far a broader dynamic range compared with a radiographic system using a conventional photosensitive film, and has a utilitarian advantage that a radiation image that is not affected by fluctuations in exposure quantity of the radiation can be obtained. In addition, the systems given above do not require, unlike the conventional photosensitive film method, any chemical treatment and has an advantage that an output image can be obtained instantaneously.
FIG. 4 is a conceptual diagram showing one example of the system using the radiation image sensing apparatus described above.
Referring to FIG. 4, the numeral 103 represents an X-ray image sensing apparatus having a built-in X-ray detection sensor 104. An object is irradiated with the X-rays emitted by an X-ray generation device 101, and the X-rays penetrating the object 102 are detected by photoelectric converting elements arranged in two-dimensional matrix form. Image signals outputted from this detection unit undergo digital image processing in an image processing unit 105, and an X-ray image of the object is displayed on a monitor 106.
Conventionally, this type of imaging apparatus has hitherto been installed in a radiation room and thus utilized. In recent years, however, a thin and light-weighted portable sensing (viewing) apparatus (which is also called an electronic cassette) comes to be demanded in order to enable various image capturing to be quickly sensed (viewed).
An outline of the configuration is now explained with reference to a side sectional view in FIG. 3. An electronic cassette 51 utilized for the X-ray imaging process described above is constructed of a fluorescent substance 51a for converting the X-rays into visible rays, photoelectric converting elements 51b arranged two-dimensionally, that serve to convert the visible rays into electric signals, a substrate 51c on which the photoelectric converting elements 51b are formed, a base 52 for supporting this substrate 51c, a circuit board 53 mounted with electronic parts for processing the photoelectrically-converted electric signals, wires 54, a housing body 55 accommodating these components, an electric power source circuit 60 for supplying the electricity to the photoelectric converting elements 51b and to the circuit board 53, and a wire 61 for the power source.
A specific configuration of the power source circuit 60 is attained by using a battery and a DC/DC power source circuit or by supplying a predetermined voltage from outside via a power supply cable (not shown) and generating a variety of voltages in the DC/Dc power source, and so on.
The thin and light-weighted portable sensing apparatus, i.e., the electronic cassette is demanded in order to enable various image capturing to be quickly sensed (viewed), however, it is required that an exposure of the X-rays and a drive timing of the X-ray sensor be synchronized.
A technology related to the synchronous timing is disclosed in Japanese Patent Application Laid-Open No. 11-151233. An explanation in Japanese Patent Application Laid-Open No. 11-151233 is concerned with a radiation sensing apparatus for obtaining an image by irradiating an object with the radiation, which is constructed of a radiation sensing unit composed of two-dimensional sensing elements arranged in a matrix form, at least one or more radiation detection units for detecting a radiation-irradiating state, a radiation irradiation timing judging unit for judging the radiation-irradiating state detected, and a drive control unit for changing an operation state of the radiation sensing unit on the basis of the judgement made above.
FIG. 5 is cited from Japanese Patent Application Laid-Open No. 11-151233. Among the numerals 150 through 158 in FIG. 5, 154 denotes a signal by which the drive control unit drives a refresh control circuit RF, and 158 denotes an operation state of the radiation sensing unit 22
Note that an idle in the operation state 158 in FIG. 5 is a state where a refresh operation is periodically executed, a sensing preparation state from performing the refresh operation described above and blank reading up till the radiation is irradiated, a sensing state is a state where a photoelectric converting operation involving the irradiation of radiation described above is conducted, and an image data output-enable state includes the photoelectric converting operation state after finishing the irradiation of radiation and also an image data output-enable state.
The radiation control unit, upon detecting the signal 150 from a radiation irradiation button, transmits a sensing request signal 151 to the drive control unit. The radiation control unit, when receiving the sensing request signal 151, refreshes the radiation sensing unit, and after having a predetermined number of blank reading operations performed, transmits a sensing ready signal 155 to the radiation control unit and at the same time, shifts the radiation sensing unit into a sensing operation.
The radiation control unit, upon detecting the sensing preparation finish signal 155 transmitted from the drive control unit, radiates the radiation from a radiation source. In FIG. 5, the numeral 153 denotes an output state of the radiation irradiated from the radiation source.
The radiation control unit finishes irradiating the radiation when an integration value of outputs from a photo timer for cutting off the X-rays with a proper quantity reaches a threshold value (a predetermined accumulated radiation irradiation quantity) or when a radiation irradiation time preset by the radiation control unit elapses.
Meanwhile, the radiation detection unit monitors the radiation and outputs in realtime an output corresponding to a dose of the irradiated radiation to the radiation irradiation timing judging unit.
The radiation irradiation timing judging unit, when the signal transmitted from the radiation detection unit 23 is less than the predetermined threshold value, judges that the irradiation of radiation is finished, and outputs a radiation irradiation finish detection signal 157 to the drive control unit.
The drive control unit, when receiving the radiation irradiation finish detection signal 157, finishes the sensing operation of the radiation sensing unit and shifts the operation to the image data output-enable state. Herein, the reason for the shift to the image data output-enable state is that the image data is not necessarily required to be output immediately after finishing the irradiation of radiation. It is, however, desirable that the image data be outputted immediately after finishing the irradiation of radiation, considering a decline of S/N ratio of the image output due to accumulation of dark currents.
As explained above, the synchronization between the radiation sensing detector and the X-ray generating device involves an execution of handshaking by a start-stop system irrespective of being wired or wireless.
Japanese Patent Application Laid-Open No. 9-73144 discloses a method of configuring the X-ray detector or photo timer disclosed in Japanese Patent Application Laid-Open No. 11-151233 give above. Specifically, it discloses a radiation detection apparatus for detecting an intensity distribution of radiation being emitted from a radiation source and penetrating an object, which includes a scintillator that emits light corresponding to the intensity distribution of radiation, an optical image detection unit having solid-state photo detection elements disposed two-dimensionally on the front surface of a transparent substrate disposed behind the scintillator, and a light quantity monitor unit disposed in rear of the optical image detection unit, for detecting a quantity of rays penetrating the substrate, of the rays emitted from the scintillator.
FIG. 6 is a view showing a configuration of a radiation sensing state of the radiation detection apparatus 3 disclosed in Japanese Patent Application Laid-Open No. 9-73144. The X-rays penetrating a grid 4 for reducing scattering reach a scintillator 5.
An optical image detector 6 (a detector for sensing) is bonded to the scintillator 5, and a plurality of solid-state photo detecting elements are formed two-dimensionally on a front surface 8a of a transparent glass substrate 8 by photolithography.
Further, a light quantity monitor unit (that is the X-ray detector or photo timer defined in Japanese Patent Application Laid-Open No. 11-151233) includes the solid-state photo detecting elements formed on a rear surface 8b of the glass substrate 8 by the photolithography, and detects rays penetrating the glass substrate 8 and reaching the rear surface 8b of the glass substrate 8, of the rays which are converted from the radiation X by the scintillator 5.
The conventional examples related to the method of attaining the synchronization between the X-ray apparatus and the sensing detector, and the layout and the configuration of the X-ray detector for attaining the synchronization, have been exemplified so far. Considering a mobile environment for the electronic cassette, however, there arises a problem that the X-ray generating apparatus can not be specified when used.
Namely, the electronic cassette is utilized in combination with a plurality of and plural types of X-ray apparatuses, and the synchronization method can not be specified. In an extreme case, neither a circuit for attaining the synchronization nor terminals might be prepared. Hence, there was needed a technology capable of a radioscopic or sensing process without the start-stop synchronization (handshaking) between the X-ray apparatus and the sensor.